[Study of the nucleation sites in collagen mineralization]

By comparing IR spectra of collagen, collagen/CaCl2 and collagen/calcium phosphate, it was found that intensities of amide I, II and III bands were significantly decreased after mineralization. Band amide I shifted to wards lower wave number. This shift indicated chemical interaction between carboxyl groups and Ca ions formed in the mineralization. The result indicated that there was another nucleation site, i.e. carbonyl [structure: see text] on collagen, besides the previous reported nucleation site of carboxyl (-COOH) on collagen. The decrease of amide I peak intensity was mainly due to blockage of C=O stretch. Comparing the IR spectra of demineralized collagen and pure collagen, amide I, II and III peaks intensity and position were almost the same. When the mineral dissolved, amide peaks rebounded, which indicated that the crystals nucleated on these sites enwrapped the groups and blocked the groups vibration. The decreases of peak intensity of amide I, II and III were different due to their different vibration modes. The result confirmed that the carbonyl group was one kind of the nucleation site during collagen mineralization. The relationship between the process of collagen mineralization and variety of amide bonds was also studied.